(1) Field of the Invention
The present invention relates to a rotary developing apparatus rotatably accommodating a plurality of developer units, a developer unit used in the developing apparatus, and an image forming apparatus having the developing apparatus.
(2) Description of the Related Art
An image forming apparatus includes a rotary developing apparatuses that accommodates developer units for respective toner colors of Cyan (C), Magenta (M), Yellow (Y), and Black (K) in a rotatable rack (hereinafter referred to as “rotary rack”), and that drives the rotary rack to rotate in order to bring a targeted one of the developer units to a designated developing position. The reduction in size and manufacturing cost has been demanded for image forming apparatuses provided with such rotary developing apparatuses. Accordingly, a simple and compact structure is demanded for the rotary developing apparatuses.
Usually, each developer unit has a toner storage and a developing chamber that receives toner from the toner storage and supplies the toner to a developing roller. However, for the purpose of the compact and simple structure mentioned as above, toner supply units tends to be omitted such as a stirring blade used for delivering the toner from the toner storage to the developing chamber. (Japanese Laid-Open Patent Application No. 2005-345536)
The simplified rotary developing apparatus works as follows. When one of the developer units is located within a predetermined rotational range as a result of the rotation of the rotary rack, the toner in the toner storage naturally falls into the developing chamber through an opening of a partition part (partition wall) between the toner storage and the developing chamber. Thus, the toner is supplied from the toner storage to the developing chamber.
FIG. 10 is an enlarged view of one of four development units accommodated in a rotary rack of a rotary developing apparatus that has been previously invented by the inventors of the present invention.
As shown in FIG. 10, a rotary rack 1032 has a rotation shaft 1033 and accommodates a plurality of developer units 1031 each storing toner of a given color (e.g. black). The rotary rack 1032 is driven to rotate about the rotation shaft 1033 in the direction of Arrow A.
Each developer unit 1031 has a toner storage 1311 that stores the toner therein and a developing chamber 1312 that is adjacent to the toner storage 1311 via a partition wall 1313. The developing chamber 1312 has a developing roller 1315 and a supply roller 1316.
When the developer unit 1031 reaches a position shown in FIG. 10 as a result of the rotation of the rotary rack 1032 (hereinafter referred to as “toner supply position”), the toner in the toner storage 1311 naturally falls into the developing chamber 1312 through a toner supply opening 1314 provided through the partition wall 1313. Thus, a given amount of the toner is supplied from the toner storage 1311 to the developing chamber 1312.
However, with the above structure of the developer unit 1031, there can be seen a significant degradation in performance of supplying the toner from the toner storage to the developing chamber 1312 when the toner remaining in the toner storage 1311 gets low.
More specifically, as the rotary rack 1032 rotates in the direction of Arrow A, the toner in the toner storage 1311 flows in the direction of Arrow B. As shown in FIG. 10, when there remains a small amount of the toner, a portion of the toner T remains in the corner 1311c upstream of the toner supply opening 1314 in the toner flowing direction in the toner storage 1311. Consequently, the toner is not sufficiently supplied to the developing chamber 1312.
As the rotary rack 1032 further rotates in the direction of Arrow A, the toner T remaining in a corner 1311c moves along an inner wall part 1311b, and falls through the toner supply opening 1314. However, it is only a small amount of the toner that falls. As the rotary rack 1032 rotates even further, a large portion of the toner T passes over the toner supply opening 1314 onto the partition wall 1313. Thus, the large portion of toner T does not fall into the developing chamber 1312.
When usable toner still remaining in the toner storage 1311 cannot be supplied to the developing chamber 1312, various problems including the following occur. The developer unit 1031 needs to be replaced earlier, which gives economical burden for users. In addition, in a case of executing job of forming monochrome images, a large number of sheets cannot be continuously printed, and therefore overall speed of image forming gets lower. Moreover, in a type of a printer that estimates, with use of a dot counter, the toner amount remaining in the developing chamber 1312 on the premise that a predetermined amount or more of the toner is supplied to the developing chamber 1312, the developing chamber 1312 becomes empty of the toner earlier than an estimated time, because a smaller amount of the toner is actually supplied from the toner storage 1311 to the developing chamber 1312 than the anticipated amount. Accordingly, the formed image can be scraped, and image deterioration may be caused.